The present invention relates to a laminar staple for joining profiled strips at an angle, particularly for manufacturing frames, frameworks and the like.
In the manufacture of picture frames or of similar wood frameworks, it is known to join strips at an angle by resorting to laminar staples inserted astride the joining plane formed by the contact of the appropriately chamfered ends of the strips. Staples of this type are disclosed in U.S. Pat. No. 1,959,360, in French patents no. 877,266 and no. 2,318,715, in Italian patent no. 1,041,695, in British patent no. 1,165,482 and in German patents no. 2,102,501 and 1,400,848.
Laminar staples are also commercially available which comprise a steel lamina folded so as to form two mutually perpendicular walls and two edge ribs or ridges which are at right angles to said walls and extend outwards, so that the staple assumes a substantially W-shaped profile. Staples of this type are disclosed in U.S. Pat. No. 29,957 and in French patent no. 2,318,715.
In order to mutually join two profiled strips, for example cut at an angle of 45.degree. in order to arrange them at right angles, said W-shaped staples are inserted astride the joining plane formed by the mutual contact of the strips, so that the edge formed by the perpendicular walls and laying at the centerline plane of the staple is at the joint.
In order to facilitate insertion, one of the borders with a W-shaped profile of the staples has a cutting edge.
Problems have been observed with these staples in keeping the strips in contact at the joining plane due to non-uniformities in their cutting and in particular to their expansion caused by the insertion of the staples.
In order to obviate this drawback, U.S. Pat. No. 4,681,498 proposed a contoured staple, but the result was positive only in the case of natural wood strips. In the case of wood pulp strips, instead, mutual contact of the strips resumes only at the upper part of the joint, whereas the lower part, which has expanded due to the insertion of the staples, remains partially open.